In this protocol, we seek to determine the frequency of chromosome aberrations in peripheral blood lymphocytes specifically associated with iatrogenic acute myelogenous leukemia using chromosome painting techniques following radiotherapy and/or chemotherapy used in the treatment of Hodgkin's disease and childhood brain tumors. We are also using blood samples from these patients to study toxicological response to carcinogen, exposure and gene rearrangements associated with deregulation of a growth promoting oncogene. Through these techniques, we hope to develop predictive assays for treatment-induced second malignant neoplasms which may lead to an improved understanding of this complication of cancer treatment and, perhaps, preventive and therapeutic strategies.